scholarly journals The carbon kinetic isotope effects of ozone-alkene reactions in the gas-phase and the impact of ozone reactions on the stable carbon isotope ratios of alkenes in the atmosphere

2003 ◽  
Vol 30 (13) ◽  
Author(s):  
R. Iannone ◽  
R. S. Anderson ◽  
J. Rudolph ◽  
L. Huang ◽  
D. Ernst
Keyword(s):  
Gas Phase ◽  
Isotope Effects ◽  
Stable Carbon Isotope ◽  
Kinetic Isotope Effects ◽  
Stable Carbon ◽  
Stable Carbon Isotope Ratios ◽  
Carbon Isotope Ratios ◽  
Kinetic Isotope ◽  
The Impact ◽  
Ozone Reactions

scholarly journals Stable carbon isotope ratios of ambient secondary organic aerosols in Toronto

2015 ◽  
Vol 15 (18) ◽  
pp. 10825-10838 ◽  
Author(s):  
M. Saccon ◽  
A. Kornilova ◽  
L. Huang ◽  
S. Moukhtar ◽  
J. Rudolph
Keyword(s):  
Gas Phase ◽  
Carbon Isotope ◽  
Stable Carbon Isotope ◽  
Isotope Ratios ◽  
Oh Radical ◽  
Stable Carbon ◽  
Stable Carbon Isotope Ratios ◽  
Carbon Isotope Ratios ◽  
Pollution Levels ◽  
Secondary Formation

Abstract. A method to quantify concentrations and stable carbon isotope ratios of secondary organic aerosols has been applied to study atmospheric nitrophenols in Toronto, Canada. The sampling of five nitrophenols, all with substantial secondary formation from the photooxidation of aromatic volatile organic compounds (VOCs), was conducted in the gas phase and particulate matter (PM) together and in PM alone. Their concentrations in the atmosphere are in the low ng m−3 range and, consequently, a large volume of air (> 1000 m3) is needed to analyze samples for stable carbon isotope ratios, resulting in sampling periods of typically 24 h. While this extended sampling period increases the representativeness of average values, it at the same time reduces possibilities to identify meteorological conditions or atmospheric pollution levels determining nitrophenol concentrations and isotope ratios. Average measured carbon isotope ratios of the different nitrophenols are between −34 and −33 ‰, which is well within the range predicted by mass balance. However, the observed carbon isotope ratios cover a range of nearly 9 ‰ and approximately 20 % of the isotope ratios of the products have isotope ratios lower than predicted from the kinetic isotope effect of the first step of the reaction mechanism and the isotope ratio of the precursor. This can be explained by isotope fractionation during reaction steps following the initial reaction of the precursor VOCs with the OH radical. Limited evidence for local production of nitrophenols is observed since sampling was done in the Toronto area, an urban center with significant anthropogenic emission sources. Strong evidence for significant local formation of nitrophenols is only found for samples collected in summer. On average, the difference in carbon isotope ratios between nitrophenols in the particle phase and in the gas phase is insignificant, but for a limited number of observations in summer, a substantial difference is observed. This indicates that at high OH radical concentrations, photochemical formation or removal of nitrophenols can be faster than exchange between the two phases. The dependence between the concentrations and isotope ratios of the nitrophenols and meteorological conditions as well as pollution levels (NO2, O3, SO2 and CO) demonstrate that the influence of precursor concentrations on nitrophenol concentrations is far more important than the extent of photochemical processing. While it cannot be excluded that primary emissions contribute to the observed levels of nitrophenols, overall the available evidence demonstrates that secondary formation is the dominant source for atmospheric nitrophenols in Toronto.

Stable Carbon Isotope Ratios in Atmospheric VOC during the EMeRGe-EU and ASIA campaigns

2020 ◽  
Author(s):  
Marc Krebsbach ◽  
Ralf Koppmann
Keyword(s):  
Carbon Isotope ◽  
Critical Role ◽  
Stable Carbon Isotope ◽  
Isotope Ratios ◽  
Stable Carbon ◽  
Air Masses ◽  
Air Samples ◽  
Stable Carbon Isotope Ratios ◽  
Carbon Isotope Ratios ◽  
The Impact

<p>VOC (volatile organic compounds) play a critical role in the chemistry of the atmosphere. The formation of many important secondary pollutants in the atmosphere, such as ozone, peroxides, aldehydes, and peroxyacyl nitrates and secondary organic particulate matter depends critically on the availability of VOC as their precursors. Many of them have strong direct adverse effects on our environment. The assessment of the impact of VOC on the atmosphere can be significantly improved by measuring their stable carbon isotope ratios. The isotopic composition of compounds emitted by natural or anthropogenic activities vary for emissions from different sources. In almost all atmospheric processes, e.g. chemical reactions, photolytic processes, transport and dilution, diffusion, and phase transitions, the isotopic ratio in VOC is altered. Studying the isotope ratios of both precursors and products makes it possible to distinguish between freshly emitted VOC and photochemically processed compounds, to increase our knowledge of transport versus chemistry, to study the ultimate fate of oxidation products, and to help assess the impact of emissions, e.g. from large population centres (MPCs), on local, regional and even global pollution.<br>The automated high volume air sampling system MIRAH has been deployed during several missions with the German High Altitude – Long-range research aircraft (HALO). Here we focus on the campaigns EMeRGe-EU and -ASIA (Effect of Megacities on the transport and transformation of pollutants on the Regional and Global scales). The objectives were to measure the pollution emitted, transported and transformed from the MPCs London, BeNeLux, Rhine-Ruhr and Po Valley for the European Part. The second part of EMeRGe was conducted from Taiwan with the goal to investigate the pollution outflow from Asian MPCs such as Taipei, Hongkong, Shanghai, Beijing, Manila, Seoul and Tokio. In both parts a key experiment was the identification of the source of the air masses by collecting whole air samples on ground prior and during particular flights in specific metropolitan regions. On 7 flights in Europe and 12 flights in Asia, mostly below 6 km altitude, more than 140 air samples were collected on HALO during each campaign, and additional 46 samples at specific ground sides. The whole air samples were analysed for mixing ratios and stable carbon isotope ratios of selected aldehydes, ketones, alcohols, and aromatics. This allowed investigating air masses of different origin, characteristic, and atmospheric processing. In this presentation we will give an overview of the data and show exemplary results.</p><p><br><em>This work was supported by the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG Priority Program SPP 1294) under grant-No. KR3861/1-1.</em></p>

scholarly journals Stable carbon isotope ratios of ambient secondary organic aerosols in Toronto

2015 ◽  
Vol 15 (11) ◽  
pp. 15431-15467
Author(s):  
M. Saccon ◽  
A. Kornilova ◽  
L. Huang ◽  
S. Moukhtar ◽  
J. Rudolph
Keyword(s):  
Gas Phase ◽  
Carbon Isotope ◽  
Stable Carbon Isotope ◽  
Isotope Ratios ◽  
Meteorological Conditions ◽  
Oh Radical ◽  
Stable Carbon ◽  
Stable Carbon Isotope Ratios ◽  
Carbon Isotope Ratios ◽  
Pollution Levels

Abstract. A method to quantify concentrations and stable carbon isotope ratios of secondary organic aerosols (SOA) has been applied to study atmospheric nitrophenols in Toronto, Canada. The sampling of five nitrophenols, all primarily formed from the photo-oxidation of aromatic volatile organic compounds (VOC), in the gas phase and particulate matter (PM) together and PM alone was conducted. Since all of the target compounds are secondary products, their concentrations in the atmosphere are in the low ng m−3 range and consequently a large volume of air (> 1000 m3) is needed to analyze samples for stable carbon isotope ratios, resulting in sampling periods of typically 24 h. While this extended sampling period increases the representativeness of average values, it at the same time reduces possibilities to identify meteorological conditions or atmospheric pollution levels determining nitrophenol concentrations and isotope ratios. Average measured carbon isotope ratios of the different nitrophenols are between −34 and −33‰, which is well within the range predicted by mass balance calculations. However, the observed carbon isotope ratios cover a range of nearly 9‰, and approximately 20% of the isotope ratios of the products have isotope ratios lower than predicted from the kinetic isotope effect of the first step of the reaction mechanism and the isotope ratio of the precursor. This can be explained by isotope fractionation during reaction steps following the initial reaction of the precursor VOCs with the OH radical. Limited evidence for local production of nitrophenols is observed since sampling was done in the Toronto area, an urban centre with significant anthropogenic emission sources. Strong evidence for significant local formation of nitrophenols is only found for samples collected in summer. On average, the difference in carbon isotope ratios between nitrophenols in the particle phase and in the gas phase is insignificant, but for a limited number of observations in summer, a substantial difference is observed. This indicates that at high OH radical concentrations, photochemical formation or removal of nitrophenols can be faster than exchange between the two phases. The dependence between the concentrations and isotope ratios of the nitrophenols and meteorological conditions as well as pollution levels (NO2, O3, SO2 and CO) demonstrate that the influence of precursor concentrations on nitrophenol concentrations is far more important than the extent of photochemical processing.

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